Catheters are well known in medicine and a wide variety exist for a variety of purposes. Catheters are typically flexible tubes of varying sizes that are inserted into the body. One common application of catheters, for example, is the removal of bodily fluids from the bladder during the time when a patient is incapacitated. As the technology of medicine has expanded, catheters are becoming more widely used for a greater variety of purposes.
Presently, catheters exist that have on their distal end a pH sensor. In these types of catheters, an electrical wire runs inside the catheter to the proximal end of the catheter. When the catheter is inserted into the body, this arrangement permits the electrical sensing of pH (that is, acidity) of the immediate environment of the distal tip. Such pH catheters are presently manufactured by Synectics A.B. of Sweden, and distributed in the U.S. by Synectics Medical, Inc. of 1350 Walnut Hill Road, Irving, Tex.
Catheters also exist that have pressure sensors at the distal tip. When these pressure sensors are inserted into the body, the local pressure around the distal tip of the catheter is able to be measured.
A lumen is a channel inside the catheter that runs the length of the catheter. Multiple lumen catheters are well known. These catheters can function much like multiple catheters with each lumen dedicated to one function. As such, a single catheter with multiple lumens can operate as a multiple function catheter. Since the diameter of the catheter is of critical importance, it becomes very difficult to incorporate a large number of lumens within a single catheter. The restriction of space availability inhibits the ability to incorporate many functions into the catheter.
Several methods are known that attempt to measure the degree of effort a patient is exerting in the attempt to breathe. The degree of effort exerted in the attempt to breathe is otherwise identified as "respiratory effort". Such methods include applying stretch sensitive belts to the outside of the abdomen, or the application of electrodes to the chest. These approaches are cumbersome and inaccurate. The most accurate technique for measuring respiratory effort has been used on a small scale basis. This technique consists of measuring air pressure in the esophagus. An effort to inhale results in an air pressure drop in the esophagus and trachea. An effort to exhale causes an increase in the air pressure in the same area. When no effort to breathe occurs, the air pressure in the esophagus will remain constant.
The prior art in the area of measuring air pressure in the esophagus consists of placing a balloon made from the finger of a latex glove on the end of an esophageal catheter. This balloon is then partially inflated. An air pressure monitor at the proximal end of the catheter connected to the balloon indicates respiratory effort. The relatively large size of the balloon often interfered with the esophageal function and other simultaneous intraesophageal catheterizations.
Soviet Patent No. 272,477, issued on May 20, 1968 to Leya and Berzinsh, teaches a stomach-intestinal probe consisting of multiple antimony electrodes to measure stomach acids and a large inflatable balloon to fix the probe in the esophagus so that fluoroscopy can be used to watch the movement of the stomach. This probe permits simultaneous monitoring of stomach acid and stomach movements. However, the balloon is relatively large and blocks esophagus function so as to break normal sleep patterns. Also, the balloon cannot function as a pressure sensor since it is too large and not connected to an external pressure monitor.
German Patent No. 2,162,656, issued to Wolters and Eckert on June 20, 1973, teaches a stomach acid gage with an electrical pH sensor. Once again, this device does not measure respiratory effort. Similar, one-function stomach acid sensors, are taught by U.S. Pat. No. 4,618,929, issued on Oct. 21, 1986, to Miller et al, and by U.S. Pat. No. 4,176,659, issued on Dec. 4, 1979 to Rolfe.
U.S. Pat. No. 4,503,859, issued on Mar. 12, 1985, to Petty, et al, teaches a device to simultaneously monitor esophageal acid and heart EKG. This device does not measure respiratory effort in any way.
German Patent No. DE 3523987A, issued on Jan. 8, 1987, to Lange, teaches a method to measure stomach function consisting of multiple pH sensors attached to the outside of a balloon on a catheter. The balloon, however, is used only to inflate inside the stomach and thereby distribute the pH sensors against the stomach wall. Normal esophageal function is blocked, pH in the esophagus is not tested, and respiratory effort is not measured.
U.S. Pat. No. 4,681,116, issued on July 21, 1987, to Settler, teaches an antimony electrode used as an esophageal electrode. This uses an epoxy resin as a sealant. This is also a single function device which does not simultaneously monitor respiratory effort.
Sleep apnea is the problem of inadequate breathing while asleep. It can have several causes, with each cause requiring different remedies. Hence, individual treatment of sleep apnea can follow only after study of the causes of sleep apnea in the individual.
One alternate cause of sleep apnea is gastroesophageal reflux (GER). GER is the process by which the subject generates acids in the stomach, which are then passed into the esophagus. These acids can then be aspirated into the lungs, causing a constriction of the trachea and difficulty in breathing. However, GER can also be a result, instead of a cause, of sleep apnea. Difficulty in breathing, caused by other reasons, can lead to increased respiratory effort in compensation. This increased effort can then encourage GER. In effect, this causes a sucking of the gastric acid into the esophagus from the stomach.
Therefore, to determine the cause of an individual case of sleep apnea, and to determine the proper remedy, it is necessary in each individual case to study and sort out the cause and effect relationship of GER and respiratory effort. In practice, this requires the accurate simultaneous measurement of intraesophageal acid and respiratory effort. Specifically, this means the accurate simultaneous measurement of pH in the esophagus and air pressure in the esophagus. It is also important that this should be done in a way that does not disturb normal sleep, and other bed activity. Unfortunately, no techniques have been developed which measure both of these factors simultaneously. As a result, the effective study and remedy of sleep apnea eludes medical science.
It is an object of the present invention to provide a catheter that simultaneously monitors intraesophageal pH and air pressure.
It is another object of the present invention to provide such a catheter that can be utilized without disturbing sleep.
It is a further object of the present invention to provide such a catheter that is compatible with fluoroscopy techniques.
It is still a further object of the present invention to provide an instrument that simultaneously monitors gastric reflux and respiratory effort.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.